Capacitive micromachined ultrasonic transducer (CMUT) devices typically include membranes capacitively coupled to underlying structures. CMUT devices have been used increasingly in medical imaging applications. For example, CMUT devices have been able to improve medical ultrasound imaging probes and to provide high-intensity focused ultrasound for use in medical therapy.
One manufacturing technique for CMUT devices uses a standard micro-electro-mechanical system (MEMS) fabrication method in which a release layer is etched out from under a layer of material, leaving a free-standing membrane. An alternative manufacturing technique involves bonding a silicon-on-insulator wafer to another structure, where removal of a handle wafer and a buried oxide layer leaves a single-crystal silicon membrane on the underlying structure.
In a typical CMUT device, individual capacitor cells are grouped into elements, and multiple elements are combined to form an array (such as a one-dimensional or two-dimensional array). One integration challenge with a CMUT array, particularly a two-dimensional array, is making electrical contact with individual cells or elements without introducing excessive parasitic capacitance and without etching a series of isolation trenches that excessively weaken the array structurally.